This Bible contradiction is from the Skeptic's Annotated Bible.
Jonah was swallowed by a big fish.
Jonah 1:17 View context
Now the LORD had prepared a great fish to swallow up Jonah. And Jonah was in the belly of the fish three days and three nights.
Jonah was swallowed by a whale.
Matthew 12:40 View context
For as Jonas was three days and three nights in the whale's belly; so shall the Son of man be three days and three nights in the heart of the earth.